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The Nature of the Cytherean Atmosphere
Albert W. Burgstahler

Searching for Hydrocarbons on Venus

Dr. Burgstahler is a professor of chemistry, University of Kansas (Lawrence). This paper is based on a presentation concerning the atmosphere of Venus given at the Velikovsky Symposium, Lewis and Clark College, Portland, Oregon, August 16-18, 1972.

Introduction

Despite being completely covered by a thick envelope of slightly yellowish clouds, the planet Venus, because of its similarity to the Earth in size and mass and the amount of energy it absorbs from the Sun (Table 1), was long believed to possess atmospheric and other properties not too unlike those of the Earth. For example, a typical view prevailing well into the present century stated: "There can therefore be no doubt that the atmosphere of Venus exerts an absorption similar to our own, and hence the nature of the two atmospheres must be similar.... condensed vapors would be naturally supposed to be situated at a considerable altitude in the atmosphere. . . . we may safely assume that the clouds of Venus consist of condensed aqueous vapor, thus again resembling those of the Earth" [1].

Table 1. Physical Properties of Earth and Venus (a)

Property Earth Venus
Average cloud cover (percent) ca. 50 100
Average albedo (reflectance) 0.35 0.77 0.07
Mean distance from Sun (miles) 92,957,000 67,200,000
Mean solar constant (ergs/cm-sec2) 1.4 x 106 2.7 x 106
Equatorial diameter at surface (miles) 7,927 7,520
Equatorial radius at surface (kilometers) 6,378 6,050 5
Oblateness (departure from sphericity) 0.003 0.000
Volume relative to Earth 1 0,855
Total mass (kilograms)b 5.976 x 1014 4.86594 x 1014
Mass relative to Earth 1 0.8149
Mean density (grams/cm3)c 5.52 5.23
Gravity at surface (feet/sec') 32.2 28.9
Escape velocity (miles/sec) 7.0 6.4
Sidereal orbital period (Earth days) 365.256 224.701
Mean synodical period (Earth days) --------------- 583.92
Mean orbital velocity (miles/sec) 18.5 21.8
Orbital eccentricity 0.0167 0.0068
Inclination of orbit to ecliptic 0 3.393
Axial rotational period (sidereal) 23h 56m 04s 243.0 0.l Earth days
Duration of solar day 24h 00m 00s 116.8 Earth days
Direction of rotation Direct Retrograde
Inclination of axis to orbit 23.5 2.2

aderived mainly from refs. 3 and 7.
bincludes atmosphere.
ccomputed from volume of solid planetary body.

Subsequently, more refined spectral investigations revealed the presence of carbon dioxide on Venus, but not even traces of water or oxygen could be detected [2].

Until about 1960 the depth and density of the Cytherean atmosphere were generally considered to be about the same as on Earth [3]. Moreover, except for a few "high" estimates, such as R. Wildt's proposal of 93 to 135C [4], the temperature at the surface was widely thought--before the advent of radiometric data in the late 1950s--to be about that of tropical or even temperate regions on Earth [5]. On the other hand, there was no agreement on how smooth or rough the surface might be [5]. Likewise, proposals for the axial rotational period varied widely, with many centering around an Earth- or Mars-like day of 24 hours, others around 15 to 30 days, and , still others favoring the planetary sidereal orbital period of 224.7 terrestrial days [6].

Thus at the time Immanuel Velikovsky's Worlds in Collision first made its appearance in 1950, few persons other than Velikovsky had strong reason to believe that Venus would prove to have an extraordinarily hot and comparatively flat surface, an extremely dense lower atmosphere, a peculiarly perturbed axial rotation, and hydrocarbon gases (or polymers) deep in its lower-lying atmosphere. Although the last of these four predictions remains in dispute and still awaits adequate testing, the first three have been amply vindicated, evidently--at least in part--to the surprise of many astronomers who had long entertained contrary views [3] [7].

Confirmatory Findings

In recent years, Earth-based studies of the microwave emission spectra of Venus, which indicate an intensely hot surface and suggest a rather dense lower atmosphere, have been fully corroborated by interplanetary space-probes. The latter show that although the temperature and pressure at the upper boundary of the main cloud layer are only about 240-250K (-33 to -23C) and 0.2 atmosphere, respectively, on both the sunlit and dark sides of the slowly rotating planet [7] [8], they soar to the neighborhood of 750K (477C or 890F) and about 90 atmospheres at the surface (Figure 1). Venera 7, which soft-landed on the nocturnal side of Venus on December 15, 1970, recorded a surface temperature of 74720K and a pressure of 901.5 kilograms per square centimeter [9]. Venera 8, which successfully landed on the illuminated limb on July 22, 1972, relayed a similar temperature, of 7438K and a pressure of 90 1.5 kg/cm2 [10].

Fig. 1. Mean middle-latitude region temperature (_______) and pressure (---------- ) profiles of the terrestrial and Cytherean atmospheres. [Data for Venus from space-probe reports; cf. refs. [7] [8], and [10].]

Mariner occultation experiments [8] and other evidence [7] also suggest that the brightly reflecting cloud envelope, with an albedo of 0.770.07 according to Irvine [11], is probably multilayered, and that its opaque portion extends to an altitude of 65 to 70 kilometers (ca. 40-43 miles). An additional overlying aerosol or haze of optically thin clouds detectable by ultraviolet photography evidently reaches to an altitude of 80-90 kilometers [7] [8].

In the upper part of the visible cloud layer, a fair amount of turbulence appears to be present, but at the height of the thin ultraviolet clouds a rapid four-to five-day equatorial planetary circulation or wave motion seems to predominate [7] [12]. This movement is retrograde (i.e., east to west) and, if real, corresponds to wind velocities in excess of 100 meters per second (ca. 230 miles per hour). Deeper in the atmosphere, as would be expected, wind movement is definitely less. At a height of 45 kilometers a lateral wind velocity of ca. 45 meters per second has been estimated from the descent pattern of Venera 8 [10]. At lower altitudes wind movement is even slower, decreasing to less than 2 meters per second below 10-12 kilometers [10].

Radar imaging [13] reveals Venus to be generally flatter than the Earth, Mars, or the Moon, with few surface-elevation differences greater than one or two kilometers (0.6 to 1.2 miles). Recently, however, numerous, large, shallow craters, 21 to 100 miles in diameter, have been shown to be present, at least in the equatorial region at 40 west longitude [14]. No agreement has been reached to account for the shallowness of these craters (the 100-mile-diameter crater being "only a quarter of a mile deep"), which obviously has important implications for their origin and history.

Other radar studies [15] indicate that Venus turns on its axis in a retrograde (east-to-west) sense with a sidereal rotational period of 243.0 0.1 (earth) days. This corresponds closely, but apparently not quite, to an Earth-locked "resonance" period of 243.16 days. With the latter, exactly the same point on the Cytherean surface would be turned toward the Earth at each inferior conjunction when Venus passes directly between the Earth and the Sun (mean synodical period occurring every 583.92 days).

Explanation Still Sought

Not surprisingly, the basis on which Velikovsky anticipated properties of this nature namely, his belief that Venus is a comparatively young planet, originating from Jupiter only a few thousand years ago, and that, within the span of recorded human history, it has had a series of enormously destructive encounters with the Earth, Mars, and the Moon as an incandescent, hydrocarbon-rich protoplanet-has not been received with much favor among professional astronomers. In general, they have preferred to consider Venus to be about the same age as the Earth and to attribute its high surface temperature not to residual natal heat, as Velikovsky proposes, but instead to an extremely efficient greenhouse effect and/or a deep-circulation, convective solar heating mechanism [7].

Venera 8 photometric measurements indicate, however, that the dense clouds allow only a small fraction of heat-producing visible and near-infrared solar radiation to penetrate to the Cytherean surface [10). Moreover, calculations show that an atmosphere such as that of Venus, consisting essentially of carbon dioxide (see below), cannot provide enough infrared opacity to maintain the observed high surface temperature [7] [16]. Water would provide much of the required extra opacity, if present in sufficient amount. However, a recent microwave study [17] of the 1.35-centimeter water absorption resonance has set an upper limit of only 0.2 percent water at almost any level in the lower atmosphere. This amount, it was concluded, is insufficient to produce dense water or ice clouds within the main cloud deck, "and it is doubtful that it may contribute significantly to a greenhouse effect," to quote the authors of the report [17].

With an opaque, highly reflecting cloud envelope (regardless of composition) insulating the surface from direct solar heating and also no doubt preventing much heat from escaping, several deep-circulation, convective heat-transfer mechanisms have been proposed to account for the high surface temperature [7] [18]. A fundamental feature of these mechanisms is that "a lateral temperature gradient is created at the surface with higher temperature on the dayside" than on the nightside [18]. It is suggested that "the deposition of solar energy at the top of the atmosphere could drive a dynamical system in which the energy is conveyed downward in a narrow region ... with rising motion at the sub [s]olar and sinking motion at the antisolar point" [19].

Owing to its enormous mass, the atmosphere of Venus has a large thermal inertia. Hence these regions of energy transfer required by convective circulation mechanisms would probably be quite difficult to detect. According to Marov [7], "during the Cytherean night ... only 0.25% of the energy store" in the atmosphere is lost. "Thus the temperature difference between the night and day sides is expected to be quite small: maximum diurnal variation at the surface should be ... <=1K" [7]. Obviously, this small a difference will be very difficult, if not impossible, to measure reliably. The close agreement of the Venera 7 nightside [9] and Venera 8 dayside [10] surface-temperature readings has already been noted. Disc-brightness measurements by Earth-based spectroscopy also show that "diurnal temperature variations are practically absent" [7].

Without regions of suitable temperature difference, a convective circulation mechanism to heat the surface cannot operate. As Velikovsky has observed [20], it violates the second law of thermodynamics to have heat transferred from uniformly colder parts of an atmosphere to portions that are uniformly hotter.

An alternative explanation for the high surface temperature of Venus has been offered by Hansen and Matsushima [21]. These authors, postulate that an internal heat source (of unspecified origin) comparable to, or up to ten times, that of the Earth can maintain the high surface temperature through the powerful insulating effect of micron-sized dust particles held aloft by turbulence. As they point out, "the most crucial question for the dust insulation model is whether sufficient wind speeds may exist near the planetary surface" to raise the required amounts of dust to the required altitudes. With the evidence from the Venera probes indicating a fairly calm atmosphere below 10-12 kilometers [10] [12], it would appear that this mechanism is also rather questionable.

Undoubtedly, other models and explanations will be proposed to account for the apparently uniform high surface temperature of Venus. However, if the planet is, in fact, of comparatively recent origin, then, as Velikovsky has suggested [22], it is probably not yet in thermal equilibrium with its environment, and it should still be cooling off. Under these circumstances, with reliable techniques, a gradual decrease in the temperature at the surface and at various altitudes in the atmosphere might be detectable. The rate of cooling will depend, of course, on how effectively the cloud cover insulates against such heat loss, but it would not seem unreasonable to expect to find a small decrease in temperature over the course of several synodical periods [23].

Atmospheric Constituents

Before considering the question of whether hydrocarbons are to be found on Venus, it will be useful to review briefly some of the information that is available about the composition of the Cytherean atmosphere and the nature of the clouds. As would be expected, the high reflectivity of the clouds makes spectral determination of atmospheric constituents difficult and complicated. Indeed, early spectral observations failed to disclose any absorption band not present in the solar spectrum, and it was not until 1932, shortly after the development of high-resolution near-infrared photographic spectroscopy, that the major constituent, carbon dioxide, was tentatively identified through three non-solar bands at 0.7820, 0.7883, and 0.8689 micron [10-1 centimeter) in the Cytherean spectrum [2]. Later investigations have fully confirmed this identification and have uncovered many additional CO2 absorption features (Figure 2). At present over 185 near-infrared absorption bands corresponding to various vibrational states of the different isotopic forms of carbon dioxide are, known [24].

Fig. 2. Near-infrared ratio spectrum, Venus/Moon. [Adapted from ref. 31, p. 98. Copyright 1971 by D. Reidel Publishing Company, Dordrecht, Holland.]

Unfortunately, it has not proved feasible to determine with certainty from spectral data alone the total or absolute amount of CO2 in the atmosphere of Venus. However, the 12C to 13C abundance ratio in the CO2 has been estimated by such means to be ca. 100: 1, or about the same as on the Earth [25]. With direct chemical sampling of the lower atmosphere by Venera probes 4, 5, and 6, CO2 has been found to be present to the extent of about 97 percent, at least in the 0.6-atmosphere region [26]. This result is based on absorption by potassium hydroxide, which measures other acidic substances besides CO2. The Soviet investigators were of course aware of this fact and noted that trace amounts of hydrogen chloride and hydrogen fluoride (Table II), which have been estimated from spectral evidence (see below), would also be absorbed but would not interfere. However, should substantial amounts of some other acidic substance(s) be present, the CO2 results would be spuriously high. No chemical analyses below the 10-atmosphere level have been made, but densimeter readings and other Venera data indicate that the proportion of CO2 probably remains essentially unchanged down to the surface [7] [9] [10] [26].

Table II. Spectroscopic Upper Limits on Minor Constituents in the Cytherean Atmospherea

 

Substance (Formula) Maximum Concentration b
Acetaldehyde (CH3CHO) 1.0
Acetone (CH3COCH3) 1.0
Acetylene (C2H2) 1.0
Ammonia (NH3) 0.03
Carbon monoxide (CO) c 50
Carbon oxysulfide (COS) 0.1
Carbon suboxide (C3O2) 0.1
Ethane (C2H6) 20
Ethylene (C2H4) 30
Formaldehyde (CH2O) 1.0
Hydrogen chloride (HCl) c 0.4-0.6
Hydrogen cyanide (HCN) 1.0
Hydrogen fluoride (HF) c 0.005-0.01
Hydrogen sulfide (H2S) 0.1
Methane (CH4) 1.0
Methyl chloride (CH3Cl) 1.0
Methyl fluoride (CH3 F) 1.0
Nitric oxide (NO) 1.0
Nitrogen dioxide (NO2) 0.01
Nitrogen tetroxide (N2O4) 0.04
Nitrous oxide (N2O) 20
Oxygen (O2) 1.0
Ozone (O3) 0.005
Sulfur dioxide (SO2) 0.01
Water (H2O) c,d 0.6-1.0

compiled from refs. [7] [24] [28] [29] [31], and T. Owen and C. Sagan, Icarus 16 (1972): 557. Up to 2% (20,000, ppm) nitrogen and other inert gases may also be present.
in parts per million, if present.
the presence of this substance appears to be definitely confirmed (see ref. [24]).
the figures represent the water in the atmosphere above the clouds (ref. [28]).Microwave data (ref. [17]) place an upper limit of 2,000 ppm water in the 0.6 to 10 atmosphere region below the visible cloud tops.

Among other constituents of the atmosphere, carbon monoxide was originally detected by its first overtone band near 2.35 microns [27]. Its volume-mixing ratio relative to the CO2 content is estimated to be about 5 x 10-5 (50 parts per million) and is apparently fairly uniform throughout the atmosphere [24]. In addition, there are three other substances positively identified by near-infrared absorption bands, with possibly higher concentrations in and below the clouds. These are water vapor (0.6 to 1.0 ppm), hydrogen chloride (0.4 to 0.6 ppm), and hydrogen fluoride (0.005 to 0.01 ppm) [24],[28] [29]). Upper limits for other possible components of the spectroscopically accessible region of the atmosphere have been established (Table II), but such information does not in any way imply the presence of these substances in these limiting concentrations. In this connection, it should be noted that the accurate determination of the amount of water vapor in the atmosphere of Venus has been especially complicated by telluric (Earth-atmosphere) water [7] [24] [28].

Venera probe analyses of the lower atmosphere indicate the presence of less than 2 percent elementary nitrogen (and other inert gases), no more than 0.1 percent free oxygen, and between 1.1 percent water at the 0.6-atmosphere level and 0.007 percent water at the 10-atmosphere level. Spectroscopically, the upper limit for oxygen above the cloud layer is 10 ppm (0.00 1 percent) [30], and for water, as mentioned above, only 0.6 to 1.0 ppm.

In contrast to the Venera findings, recent microwave studies cited earlier [17] suggest a maximum of 0.2 percent water in the same altitude region in which the Venera probes recorded up to 1.1 percent water (ca. 45 to 55 kilometers). As already indicated, these microwave results are interpreted [17] as excluding the possibility of water or ice clouds in the lower atmosphere, in agreement with a similar conclusion based on near-infrared evidence [24] [28].

Although spectral data reveal an upper limit of 0.03 ppm ammonia relative to CO2 in the atmosphere above the clouds [31], photo-resistance measurements of color-change indicators on board Venera 8 are reported [10] to have recorded between 0.01 and 0.1 percent [100 to 1000 ppm) free ammonia during the descent of the spacecraft through the 46- to 33-kilometer altitude region. In view of the fact that larger amounts of HCl than ammonia are present above the clouds, these findings, if valid, suggest that the clouds may act as a barrier to the movement of ammonia to higher altitudes (see further discussion below). In any event, ammonia (and certain of its compounds) would be expected to interfere with the methods employed in previous Venera missions to determine the water content of the Cytherean atmosphere [7] [26] and thus might account in part for the differing results of the Venera and microwave analyses for water.

Sulfuric Acid Clouds?

Many different substances have been proposed for the visible clouds of Venus [31] [32], but none of them quite meets all the requirements of the currently available data. In addition to specific spectral requirements in the visible, ultraviolet, and infrared, optical polarization measurements show that the cloud particles are spherical with a narrow distribution of radii near 1 micron. Moreover, in the region of maximum albedo at a wavelength of 0.55 micron, they exhibit a refractive index of 1.450.02 [33], revised recently to 1.440.015 [34]. This is much too high to be compatible with that of pure water (1.33) or ice (1.31) at 0C. Actually, any deviation greater than 0.01 from 1.44 introduces marked disparity between the calculated and found polarization. Sphericity of course strongly implies that the particles are liquid droplets. However, considering that the temperature of the upper regions of the clouds is uniformly ca. -23C [34], only a very limited number of possible candidates would appear to meet this requirement.

Solutions of HCl in water, for example, as proposed by J. S. Lewis [35], either have too low a refractive index and too high a vapor pressure of water or else, if highly concentrated, have too high a vapor pressure of HCl to be compatible with observed cloud-region values [24] [28] [34]. In addition, although they exhibit some of the spectral features of Venus [35], aqueous HCl solutions particularly lack the absorption bands found in the 9.5- and 11.2-micron region of the Cytherean spectrum [34] [36].

The same spectral shortcomings apply to most other candidates including ammonium bicarbonate [37] and the related carbamate, which obviously are logical entities for consideration in view of the Venera 8 data indicating the presence of ammonia in the 46- to 33-kilometer region. The high thermal lability of these substances provides a plausible mechanism for keeping them aloft by dissociation and recombination at lower and higher altitudes, respectively. On the other hand, because. they are solids at the temperature of the upper surface of the clouds, these materials would not appear able to match the polarization data nearly so well as would a liquid condensate, even assuming satisfactory agreement with the observed refractive index [37].

Various organic compounds, including certain types of unsaturated hydrocarbons, have refractive indices and volatility properties that are reasonably consistent with those of the cloud particles. Some of them also possess at least part of the ultraviolet absorption displayed by Venus. However, none have been found which do not appear to be excluded by the absence of requisite bands in the near infrared (see next section).

In apparent contradiction to the Venera 8 report concerning the presence of ammonia in the lower Cytherean atmosphere, a proposal has been advanced by G. T. Sill and developed recently by A. T. Young [34] that the cloud particles consist mainly of 75 percent sulfuric acid (by weight) in water. At the temperature of the upper part of the clouds (ca. -23C), 75 percent H2SO4 has a refractive index of 1.44, the very same value observed for the clouds. As a liquid at this temperature, it can be expected to exist as spherical droplets. Its equilibrium water vapor pressure is only one hundredth that of pure water or ice, thereby accounting for the relatively small quantity of water found in the region of the clouds.

Equally striking is the fact that 75 percent H2SO4 exhibits an infrared spectrum that is remarkably similar to that of Venus (Figure 3), with prominent absorption bands at 9.5 and 11.2 microns as well as in the 3-4 micron region [34]. In the lower regions of the atmosphere, where high temperatures prevail, the dissociation of H2SO4 into water and sulfur trioxide would serve as a mechanism to recirculate its components back to cooler, higher altitudes for recombination as a dense mist and reformation of liquid droplets.

Fig. 3. Infrared spectra of carbon dioxide (gas), Venus, and 78.5% aqueous sulfuric acid. [CO2 spectrum adapted from Sadtler Standard Infrared Spectra No. 1924. Copyright 1962 by Sadtler Research Laboratories. Permission for the publication of Sadtler Standard Spectra has been granted, and all rights are reserved by Sadtler Research Laboratories, Inc. Spectra of Venus and 78.5% H2SO4 adapted and redrawn from ref. [34], copyright 1973 by Academic Press.]

Only the short-wavelength absorption of Venus in the near-ultraviolet, which produces the light yellowish color, is not accounted for by strong solutions of sulfuric acid in water. Unless some additional substances are present, such solutions are transparent in this region. One possibility that is considered attractive [34] is iron(II) sulfate monohydrate, since its short-wavelength reflection spectrum is similar to that of Venus [38]. Iron(III) chloride, along with photo-dissociation of HCl in the upper atmosphere to produce chlorine and HOCl (by reaction of chlorine with water), has also been proposed to account for the yellowish color resulting from the increased absorption at shorter wavelengths [35] [39]. The nature of the high, optically thin "clouds" or haze above the visible cloud deck is still obscure [34].

Although it is argued [34] that there is no overriding chemical incompatibility between sulfuric acid and the other known constituents of the Cytherean atmosphere, the co-existence of free ammonia with an excess of sulfuric acid, as already noted, would appear to be contraindicated. Moreover, the view has been expressed [28] that sulfuric acid clouds must "most certainly be rejected, due to the other chemical complications this model would create." On the other hand, the cosmic abundance of sulfur in relation to the small amounts apparently needed to produce the observed cloud opacity does seem to be compatible, since a mixing ratio of H2SO4 to CO2 ranging from only 3-3000 ppm is held to be required [34].

One other implication of sulfuric acid clouds which should be mentioned is the fact that in the hot, lower regions of the atmosphere, sulfuric acid and its dissociation product, sulfur trioxide, would be expected to behave as strong oxidizing and sulfonating agents. They would therefore be incompatible with the sustained presence of any readily oxidizable substances, such as hydrocarbons and their derivatives. A related argument has been advanced previously in connection with the relatively small amount of carbon monoxide in the Cytherean atmosphere [40]. Under high temperature conditions, the amount of CO present presumably would be much larger if reducing agents such as hydrocarbons were available to enter into equilibrium reactions with CO2.

Hydrocarbons Present?

On the basis of the considerations just mentioned, it would appear that there is not much likelihood of finding any significant amount of hydrocarbons on Venus at the present time. Of course, this does not mean that hydrocarbons could not have been present at some time in the past. It has been argued, for instance, that photodissociation of water in the upper atmosphere of Venus, followed by escape of hydrogen from the planet, might even today be generating oxygen for the conversion of hydrocarbons to CO2 and water [40] [41].

In any event, if the Venera 8 analysis of ammonia in the lower atmosphere is essentially valid, then the fact that only traces of ammonia can be detected spectroscopically in the region above the clouds is no proof that more substantial amounts are not present at lower altitudes. Hence it is legitimate to ask: are other substances possibly present in the clouds or lower regions of the atmosphere that are not yet recognized through Earth-based spectroscopic observations? Assuming for the moment that Velikovsky's proposal for its origin by cleavage from the planet Jupiter is basically sound, then Venus might well be expected to have not only ammonia in its atmosphere, as found on Jupiter, but also hydrocarbons, such as methane (or derivatives thereof), which are also present in the Jovian atmosphere.

As indicated in Table II, at most only trace amounts of low-molecular weight hydrocarbons appear to be present in the Cytherean atmosphere above the clouds. This conclusion is based largely on the absence of various C-H stretching overtones and combination bands (Figure 4) in the high-resolution near-infrared spectrum of Venus (Figure 2). Unfortunately, the many intense CO2 lines in this spectral region make detection of the generally weak C-H (and related N-H and O-H) overtone and combination bands extremely difficult and uncertain. Such bands often coincide with positions of CO2 bands or at best can be expected to occur as poorly resolved shoulders on them. At the present time, however, virtually all previously unidentified bands [42) in the near-infrared spectrum of Venus have been shown to belong to CO2 [43).

Fig. 4. Chart of characterizing near-infrared bands. [Adapted and redrawn from W. Kaye, "Near-Infrared Spectroscopy," Spectrochimica Acta, 6 1954 , p. 281. Copyright 1954 by Pergamon Press, Ltd. Reprinted with the permission of Microform International Marketing Corporation, exclusive copyright licensee of Pergamon Press Journal back files.]

In the infrared proper (2.5 to 15 microns), hydrocarbons and their derivatives display much stronger C-H absorption bands than in the near infrared. In particular, the strong fundamental C-H stretching modes in the 3.2-3.5 micron region (3125-2850 cm-1 ) are especially useful. This portion of the Cytherean spectrum (Figure 3) shows intense, poorly resolved absorption, only a small portion of which can be due to CO2 (weak band at 3.4 microns). Certain types of compounds entirely lacking in C-H bonds, such as weak and strong acids (H3O+ ion), ammonium salts, bicarbonates, and certain metal ion hydrates (e.g., Fe++), also exhibit strong absorption in this region. Hence, although the origin of these bands in the spectrum of Venus is still uncertain, they are not inconsistent with an assignment to C-H stretching modes.

The intense absorption at 4.3 microns in the infrared spectrum of Venus is clearly due to the fundamental C=O asymmetric stretching vibration of carbon dioxide. Additional CO2 bands occur at 2.7, 2.8, 13.9, and 15 microns, with weaker bands at 12.6, 13.5, and 13.7 microns. The strong band at 15 microns is due to the principal scissoring (bending) vibrations. Broad absorption in the 8-10 micron region may in part be due to hydrated CO2, but it would also result from C-O and C-N bond stretching that would be expected of various derivatives of hydrocarbons such as alcohols, ethers, esters, amines, etc.

Although the refractive index data would appear to exclude most types of aromatic (benzenoid and/or heterocyclic) compounds from the cloud layer, olefinic substances, if present in this region of the atmosphere, could have the observed refractive index and might also exhibit some of the ultraviolet absorption properties. They would also be expected to display fairly strong C-H out-of-plane deformation vibrations in the 10-14 micron region as well as double-bond stretching and other types of C-H absorption in the 6-8 micron region of the infrared spectrum.

As seen in Figure 3, the infrared spectrum of Venus exhibits a significant amount of absorption in the regions just mentioned--absorption that is not due to CO2 sulfuric acid, or other known constituents of the atmosphere [34]. Assignment of at least a portion of this absorption to olefinic and/or other organic compounds is not unreasonable (if sulfuric acid is not present!). But without confirmatory evidence in the near-infrared, no firm conclusion along such lines can be drawn.

In an attempt to demonstrate the presence or absence of hydrocarbons in the upper levels of the clouds, W. T. Plummer [44] measured the reflectance-absorption spectra of various paraffinic hydrocarbon frosts. He reported a marked depression in reflectivity in the 2.3-2.5 micron region which is not observed, or rather, observed less strongly, in the near-infrared spectrum of Venus.

The infrared evidence for hydrocarbons in the spectroscopically accessible regions of the Cytherean atmosphere is therefore tenuous at best. Nevertheless, the possibility of finding hydrocarbons in the lower parts of the atmosphere beneath the clouds cannot be dismissed. As L. D. Kaplan has pointed out [45], the microwave emission spectra of Venus show a double maxima in rotational temperature distribution that "implies a stratified cloud layer at a level corresponding to a temperature of about 400K" (127C). In his view, "All molecules that are likely candidates for condensation or polymerization at this temperature have CH bonds, and therefore absorb strongly around 3.5 ... The problem now is to account quantitatively for the very great opacity of the lower atmosphere by identifying the absorbing gases. . . . "

Future space-probe investigations of Venus will obviously be called upon to achieve this goal.

Questions and Conclusions

Today much is known about our nearest planetary neighbor that was not known or widely recognized just a few years ago. At a time when quite contrary views prevailed, Velikovsky made the bold claim that Venus would prove to be extremely hot and that it has a massive atmosphere which in times past gave evidence of being rich in hydrocarbons. The first two parts of this claim have been remarkably vindicated, and at least an enormous quantity of oxidized carbon (CO2) has been demonstrated to be present in the Cytherean atmosphere.

However, many important questions remain. We still do not know for certain whether the deep, lower-lying atmosphere contains hydrocarbons besides carbon dioxide. Not only is it most urgent that this question be resolved,, but also whether the ammonia reported by Venera 8 is really present and whether the clouds do, in fact, consist of sulfuric acid droplets, as has been proposed recently.

In addition, we are still uncertain about the origin and constancy of the high surface temperature, the evolution of the large, shallow craters, the intimate workings of the atmospheric circulation, the reason for the essentially Earth-locked retrograde axial rotation, and the cause of the constantly recurring, planet-wide variations in the height of the cloud cover that have been verified recently [46].

Finally, with reference to Velikovsky's postulate of the origin of Venus from Jupiter--which, as we have seen, has obviously scored some very impressive successes in predicting recent discoveries about Venus--how does it happen that at present the planet is so rich in carbon dioxide but apparently not in hydrocarbons, at least in the region of the cloud tops? Moreover, why is there so little water in the Cytherean atmosphere?

Various answers to these questions have been proposed. If the CO2 (and also the HCl and HF) came mostly from volcanic activity, then substantial amounts of water should likewise be present. But if the atmosphere originally contained or later acquired relatively large amounts of water, what has become of it? One view is that the water has undergone photo-dissociation in the upper atmosphere at a rate sufficient for loss of most of the hydrogen from the planet into outer space. But then what became of the resulting oxygen? (It is too heavy compared to hydrogen to escape easily.) Were reduced forms of carbon present that were then oxidized to CO2, as has been suggested [40] [41]?

In his partial reconstruction of its history in Worlds in Collision, Velikovsky proposed that Venus had a number of atmospheric-interaction and exchange contacts with other celestial bodies during the, centuries before it was brought into its present nearly circular orbit around the Sun. These encounters could thus account for the acquisition of water (or oxygen) needed to convert the original Jovian mantle of hydrocarbons on Venus into carbon dioxide.

However, the proposed loss of large amounts of hydrogen to space by photo-dissociation of water in the upper atmosphere suggests that the ratio of deuterium to hydrogen in the lower atmosphere should be significantly higher on Venus than on Earth, since the latter has retained such a large quantity of water on its surface. In fact, the search for DCl and HOD in the near-infrared spectra of Venus has not yet disclosed the presence of even the detection limit of a 1:10 ratio of deuterium to hydrogen in the lower atmosphere [47]. Likewise, a reinvestigation of the far-ultraviolet spectrum of the upper atmosphere of Venus by means of an Aerobee 150 rocket [48] has not confirmed the deuterium enrichment that was derived earlier from the Mariner 5 data [47] [49].

Thus the interrelated problems of the origin of the carbon dioxide, the possible presence of hydrocarbons-now and/or in the past, and the comparative lack of water in the atmosphere of Venus do not appear to have been adequately resolved. However, judging by the rapidity with which major advances in our knowledge about the planets have been occurring in recent years, it seems more than likely that satisfactory solutions will soon be forthcoming.

Acknowledgments

I am deeply grateful to various colleagues for their many valuable suggestions and to Dr. L. D. G. Young for her most helpful comments on an earlier draft of the manuscript.

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[48]   L. Wallace et al., Astrophys. J. 168 (1971): L29.

[49]   L. Wallace, J. Geophys. Res. 74 (1969): 115; T. M. Donahue, J. Geophys. Res. 74 (1969): 1128;.J. Atmos. Sci. 25 (1068): 568.

PENSEE Journal VI

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